1. Field of the Invention
The present invention relates to an electrolytic gas generation method and electrolytic gas generation device for generating ozone gas by electrolysis, and more specifically, relates to an electrolytic gas generation method and electrolytic gas generation device for making ozone generation more stable and for generating high concentration ozone gas.
2. Description of the Related Art
Generation of ozone gas by electrolyzing water has been performed from more than 100 years. Formerly, dissolution and electrolysis for electrolyzing a solution including an anion having a high electronegativity to generate ozone was used. However, with the recent development of solid polyelectrolytes, an ozone generation device which uses electrolysis of water using the solid polyelectrolyte has been produced and put on the market.
Electrolysis of water using a so-called zero cap method, in which a perfluorocarbon sulfonate type cation-exchanger membrane is used as a solid electrolyte, and an anode and a cathode are closely arranged on the opposite sides thereof, has a simple structure and is easy to handle, having no corrosiveness except in the case of the ozone gas. Therefore, this method becomes dominant in the recent ozone generation by the electrolysis of water.
The concentration of ozone gas is about 20%, with the remainder being oxygen gas containing saturated vapor, and hence the ozone gas is a mixed gas of ozone and oxygen and hardly contains impurities.
Therefore, the use of ozone has been widely spread not only in the field of sterilization but also in the field of washing semiconductors recently. There is a disadvantage in that the power consumption slightly increases, as compared with a silent discharge method in which ozone is generated by using oxygen as a raw material, and applying a high frequency voltage thereto, but since the ozone gas concentration is high, its solubility in ultrapure water is high, giving an advantage in that high purity and high concentration ozone can be easily produced.
However, as the density of a semiconductor increases, microfabrication is required and, particularly, requests for washing accuracy has increased recently.
Moreover, the water quality of ultrapure water is improved with microfabrication, and ultrapure water without containing metals or organic matter at all has been generated and used.
In ozone generation by electrolysis, a change in the water quality of pure water, being, still now, a raw material, affects the ozone gas generation, thereby causing a change in a bath voltage, and a fluctuation in the ozone gas concentration.
Particularly, a fluctuation in the ozone gas concentration causes an instability in washing, and becomes a cause of insufficient washing. Therefore, stability in the ozone gas concentration has been strongly demanded (for example, see Japanese Patent Publication No. 2002-166279, pp 1 to 5, FIGS. 1 to 2).